With California's drought stretching through its fourth year, the sight of water gushing out of Palo Alto's construction sites has drained the patience of Keith Bennett and his neighbors in the Crescent Park, Old Palo Alto and Community Center neighborhoods.

The water they're concerned about comes from the ground rather than the sky, and its flow is caused not by Mother Nature but by local property owners building basements in their homes. When the construction occurs in areas with shallow groundwater -- particularly in neighborhoods closer to the Bay or creek beds -- builders set up wells to pump out the water, sending it into the city's storm drains and, ultimately, the Bay.

Basement construction makes all the sense in the world for property owners because the city's zoning regulations don't include basements in calculating the density that is allowed for new homes. And with the city's property values soaring, building down is both a legal and logical option for increasing property values.

While a 2008 report from the Public Works Department stated that the city typically approves between five and 10 dewatering permits per year, in 2015 the number of such projects was 13, according to a new report.

In recent months, the gushing groundwater caught the attention of Bennett and many others, who argue that dewatering degrades the environment, causes land subsidence and wastes thousands of gallons of water at a time when residents are being encouraged to conserve.

Now, Bennett's new grassroots group, Save Palo Alto's Groundwater, is calling for the city to adopt an immediate moratorium on the practice. Over the past several months, he has been attending City Council meetings to bring attention to the topic.

Earlier this month, the group submitted a petition with about 200 signatures, asking the city to ban groundwater pumping until new laws are in place for preserving groundwater as an emergency water-supply resource during a drought; mitigating the impacts of pumping on the aquifer; and addressing the impacts of the activity.

"Water is too precious a resource to be wasted, and current city policies regarding dewatering do not take into account the possible need of this water to mitigate future droughts nor its beneficial effects of supporting our canopy, our properties and our infrastructure," the petition states.

The subject of groundwater pumping, like the water itself, has resurfaced periodically in Palo Alto during the past two decades. The city commissioned analyses on the topic in 2003 and 2004 and last held a public hearing on the issue in 2008, when the Planning and Transportation Commission discussed it. Then, as now, the hearing was prompted by complaints from citizens about the impacts of the practice on water supply, land subsistence and trees.

This year, with the drought firmly in place and basement construction on the rise, the chorus of complaints has been getting louder and louder.

Elizabeth Whitson, who lives on Webster Street, said the increase in the number of houses being replaced has been noticeable in the Old Palo Alto neighborhood, as has the groundwater pumping.

"At one particular house just down the street, they were pumping for about three months earlier this year," Whitson told the Weekly. "You just saw all this water getting tubed from this house to make up a basement and just going to the sewer and the Bay in the middle of the drought. All of us were wondering how the city allows this."

Bennett noticed something was awry in 2011, when a homeowner a few doors away was installing a basement and began a dewatering operation. After about three weeks, Bennett noticed that he could no longer open the front door to his Webster Street home, he told the Weekly. This persisted for a few months. Then the dewatering stopped. The door began to open again.

Unsure about the correlation, Bennett didn't pursue the subject until April of this year, when another nearby homeowner began a dewatering operation. This time, the patio door to his house wouldn't open, he said. By the middle of the summer, another door leading to the patio wouldn't close flush anymore and the brick on his front porch had settled about an inch, he said.

Bennett began talking to his neighbors. One reported that his house experienced cracks in 2008, when another groundwater pumping operation was taking place. Bennett began digging through the city's dewatering studies, reviewing the city's rules and conceptualizing exactly how much water is being pumped from the shallow aquifer. Relying on an estimate from the city's consulting engineers (which determined that each basement construction results in between 8 million and 10 million gallons of water getting pumped), he determined that the recent basement boom caused more than 100 million gallons of groundwater to be pumped from the shallow aquifer and sent to the storm drains and the Bay.

Now, Bennett hopes that city officials will start treating this water like the precious resource he and his neighbors believe it is.

He also wants to make sure that, until the city studies the issue further, no more permits will be issued for dewatering operations. Under existing laws, dewatering isn't permitted between October and April anyway but, as Bennett noted, contractors can take out permits any time for pumping in the spring. On Nov. 9, he presented the petition to the council. He also created the website, savepaloaltosgroundwater.org, to consolidate all the recent studies and to keep the community updated on the efforts to learn more about the impacts of basement construction.

"They're like great big dams in the soil, and they affect water flows," Bennett said. "And the city wants to say, 'No they don't.'"

With dozens of other residents making similar concerns throughout the spring, summer and fall, Public Works officials created an FAQ (frequently asked questions) page to address the topic, including explaining how dewatering works and the city's current permitting process for allowing the practice. And on Dec. 1, the City Council's Policy and Services Committee will dive deeper into the subject of groundwater and consider possible changes to the city's process for granting permits for basement construction that requires dewatering.

So far, however, Public Works staff have rejected residents' common assertion that the volume of groundwater being pumped from the city's shallow aquifer is sufficient to cause land subsistence or other lasting damage. The aquifer that contains the pumped-out groundwater sits above the much deeper and larger aquifer that acts as Palo Alto's emergency-water supply, said Assistant Public Works Director Phil Bobel, who asserted in numerous response letters to concerned residents that it would require more wells and longer periods of pumping to cause subsistence.

When resident Valoran Hanko warned that the groundwater pumping would change the elevation in the neighborhood, Bobel replied that the pumped-out water would simply be replaced with new groundwater.

In another letter, Bobel challenged the notion that the pumped-out water is being "wasted." Rather, he wrote to resident Georgia Relsman, the water ends up going to the creeks and the Bay -- the same place where it would end up if it remained in the aquifer.

"The pumping and the discharge of this shallow groundwater to the storm drains sends the ground water to the same place, our creeks and Bay, where it supports ecosystems and their wildlife."

Even so, Bobel wrote, the city is working with builders to "try to get as much of water used as practical."

"The main limitations are the very high cost of trucking the water and the lack of a piping system from the pumping sites," Bobel wrote.

At the same time, the city has been looking for new ways to use the water. In the summer of 2014, Public Works unveiled a "truck fill" station at a dewatering site. The water, while not potable, could then be used for efforts like irrigation and dust control, according to the city officials.

The city also now requires all contractors to have the pumping systems fitted with valves and connections to enable city crews to fill water trucks and other containers. The city now has six such pumping stations at 1405 Harker Ave., 1820 Bret Harte St., 804 Fielding Drive, 713 Southampton Drive, 3932 Grove Ave. and 2230 Louis Road.

While Public Works is not recommending any new restrictions on groundwater pumping, staff is recommending that the city's Basement Pumping Guidelines be broadened to "specifically require a determination of impacts of groundwatering pumping on adjacent buildings, infrastructure and trees and landscaping."

Under this proposal, applicants would determine the "approximate location of the temporary cone of depression caused by pumping," according to the Public Works report. Avoidance measures would be required if impacts are anticipated.

The department's list of additional proposed program improvements includes more public outreach to encourage fill-station use; increasing outreach about water flow to the city's storm drains, creeks and bay; and new specifications for fill stations to enable enough water pressure to accommodate multiple users. Staff also recommends exploring refinements for "use plans" submitted by contractors, with the aim of maximizing on-site water use.

The report also notes, however, that contractors have advised staff that imposing new requirements to use groundwater could "increase pumping duration and project cost." One contractor also said that users "could be injured at fill stations, leading to potential liability."

The measures, which the council committee will discuss, fall far short of the type of moratorium that residents like Bennett are recommending. At the Oct. 5 meeting of the City Council, Bennett argued for a new study of dewatering, noting that the city's last analysis was conducted more than a decade ago, when conditions were different.

"Only if such a study shows that the effects are negligible, and city policies are revised to ensure mitigation of the effects, should dewatering be permitted to continue," Bennett told the council.